A piston compressor of this kind is known from U.S. Pat. No. 5,842,420. The crank shaft is driven by an electric motor. In this connection, the crank pin orbits around the axis of the crank shaft. By means of the connecting rod, this orbiting movement is transferred to a piston, which then reciprocates straightly in a cylinder. The lower end of the crank shaft is submerged in an oil sump. Through the rotation of the crank shaft and the resulting centrifugal forces in the oil channel arrangement, the oil from the oil sump can be conveyed to the crank pin. From here the oil leaves through an opening of the oil channel arrangement in the circumferential surface of the crank pin with the main purpose of lubricating the bearing surface between the crank pin and the second connecting rod eye. On each rotation, the opening once comes to overlap the longitudinal channel, so that a short oil supply or pulse also reaches the first connecting rod eye with the purpose of lubricating the bearing surface between the first connecting rod eye and a bearing pin arranged in the piston.
A similar embodiment is known from U.S. Pat. No. 5,093,285. Further to the longitudinal channel in the connecting rod shank, additional channels are provided in the connecting rod, which channels end on the outside of the connecting rod and are directed into a piston chamber, in which the piston pin is arranged.
Another kind of lubrication is shown in DE 195 16 811 C2. Here, a sleeve is arranged between the second connecting rod eye and the crank pin, which sleeve projects in the axial direction from the crank pin and forms a reservoir, into which the oil channel arrangement opens. From the reservoir the oil can flow downwards to lubricate a bearing surface between the sleeve and the crank pin. This document says nothing about a lubrication in the area of the first connecting rod eye.
In the known compressors, whose connecting rods have a longitudinal channel, there is a problem in that the lubricating layer between the second connecting rod eye and the crank pin is weakened particularly in the areas, in which a relatively large load must be adopted. This is caused by the fact that the place where the oil is supplied cannot be chosen at will. During operation the oil is transported by the centrifugal force, which requires that the outlet of the oil channel arrangement is radially offset in relation to the centrically arranged suction position. When the radial offset is too small, the pumping effect is too weak. This then causes that the outlet of the oil channel arrangement practically always overlaps the longitudinal channel of the connecting rod shank, when the piston is close to or in the upper dead centre. However, at this instant, the load is the largest.